For performance monitoring of 10 Gb/s (future 40 Gb/s) transmission systems, it is mandatory to obtain a reliable estimate of the status of optical transmission links for preemptive fault detection for network management or network control. This status can be described by optical link parameters being characteristic of the distortion of an optical signal transmitted through the optical fiber link, such as chromatic dispersion (CD), polarization mode dispersion (PMD), self-phase modulation (SPM), etc.
There have been proposed many costly solutions for performance monitoring of optical links, including optical measurement techniques as well as techniques which use additional modulation tones (not in the standard). At the ECOC 2004, M. Wrage and B. Spinnler have proposed a method of distortion identification by analyzing equalizer coefficients (FFE tap settings) of a finite impulse response (FIR) equalizer in the paper “Distortion Identification in WDM Networks by Analysis of Electrical Equalizer Coefficients”. The solution proposed in this paper is based on the equaliser setting of a FFE, which is used for all signal bit patterns. Due to the limited parameter set (taps) it works only for a limited dispersion range or fails if mixed distortions are present (e.g. PMD and CD).